Thiol end groups

Diisocyanates or Polyisocyanates. The thiol end groups of the hquid polysulfides are quite reactive with isocyanates (eq. 3). Typical chisocyanates, such as 1,3-toluene chisocyanate (m-TDl) and diphenylmethane-4,4 -diisocyanate (MDl), ate effective in curing hquid polysulfides. Using hquid polysulfides in-... 

Reactions of the Disulfide Group. Besides the thiol end groups, the disulfide bonds also have a marked influence on both the chemical and physical properties of the polysulftde polymers. One of the key reactions of disulfides is nucleophilic attack on sulfur (eq. 4). The order of reactivity for various thiophiles has been reported as (C2H O) P > R, HS , C2H5 S- >C,H,S- >C,H,P,... 

RAFT polymerization lends itself to the synthesis of polymers with thiol end groups. Several groups have utilized the property of thiols and dilhioesLers to bind heavy metals such as gold or cadmium in preparing brushes based on gold film or nanoparticles1 8 761 763 and cadmium selenide nanoparticles.763 76 1... 

The synthesis of polysulfide elastomers involves the use of a small amount of trichloroalkane in addition to dichloroalkane and sodium sulfide in order to form a branched polymer. The prepolymer is treated with a mixture of sodium hydrosulfide and sodium sulfite followed by acidification to convert all end-groups to thiol groups. Further polymerization and crosslinking is achieved by oxidative coupling of the thiol end-groups by treatment with lead dioxide, p-quinone dioxime, or other oxidizing agent... 

The molecular models are in a sense a subset of the geometrical ones - we assume that we know which molecules are present and we assume that we know their geometries (indeed sometimes we assume more than that, such as the usual assumption that thiol end groups lose their protons when forming their asymmetric bond with gold). In this we also necessarily assume that there are no other species, either on the electrode surface or in the surrounding media, that influence the current flow through the system. 

Two-fold Menschutkin reactions on 4,4 -bipyridine provide a route to compounds containing a redox-active paraquat unit [15]. Thus, reacting 54 with 6-to-syloxyhexyl thioacetate afforded 55 (Scheme 10.17). Perylene tetracarboxylic dii-mide presents another electron acceptor that has been functionalized with thiol end-groups. Thus, heating a mixture of the dianhydride 56 and 4-aminothiophe-nol (57) gave the product 58 (Scheme 10.18) [16],... 

Ritter reported a radical chain transfer agent as a dual initiator 7 [26], The first step builds on the fact that hydroxyl groups are much better nucleophiles in enzymatic ROP than thiols. Due to the chemoselectivity of the enzyme, PCL with predominantly thiol end-groups were obtained, which were subsequently used as a macroinitiator for styrene. The authors further report that the reaction yield can be further increased by microwave irradiation. While thiols provide less control over the radical polymerization than RAFT agents, the subsequent radical polymerization successfully lead to the synthesis of poly(CL-b-styrene). 

Polysulphide rubber, thiol end groups Thiokol LP Thiokol- Morton Polyamides, polychloroprene... 

The desired end-groups can be introduced after the living polymer-monomer equilibrium is reached. The preparation of polyTHFs, terminated at both ends with primary amino, bromine, isocyanate, and thiol end-groups, has been described by Smith and Hubin5). 

Insertion at the thiol end groups with elimination of hydrogen sulfide... 

Assuming that hydrogen abstraction from the hydrocarbon backbone of the polymer does not occur, the evolved hydrogen sulfide must be formed by interaction of thiol end groups. 

This elastomer which was introduced commercially in 1929, had limited use until liquid polymers with reactive thiol end groups were obtained by the reduction of this elastomer. The liquid polyethylene sulfides are readily oxidized and cured by the addition of oxidants, such as lead peroxide.22... 

Ordering of terminally functionalized DLCs as self-assembled monolayer (SAM) on different substrate surfaces has been investigated. Triphenylene derivatives 34-36 (Scheme 7.10) with one or two thiol end groups align homogeneously... 

Alternatively, Whittaker et al. utilized the reversible oxidation/reduction of a thiol-terminated linear polymer as a homocoupling reaction to access macrocycles that could be reversibly cyclized and cleaved (Scheme 12.5) [29]. The linear precursors were prepared using reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene from a bifunctional initiator (16). The desired polystyrene with thiol end groups could be isolated in near-quantitative yields by aminolysis of the polymer with terminal dithioester groups (17). The linear dithiols... 

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